The 2015 will have trailer ratings in it's manual.
8000 is the GVWR weight class (Gross Vehicle Weight Rating)-- which is not the trailer weight permissible.
Trailer tow rating in 2015 manual also depends on which box (standard or short) the truck has.
2015 cc 4x4 v6 - shows 7000 lb with std box, and shows 7100 with short box.
The 2015 manual can also be downloaded from GM if you don't have the one that came with the truck.

If the 1997 manual, isn't available, it can be downloaded here:
https://my.gmc.com/content/dam/gmownercenter/gmna/dynamic/manuals/1997/gmc/sierra_1500/1997_gmc_sierra_owners.pdf
page 4-48 has the engine/trans/rear end combos that were available, an towing rating for each one.
There was no 4.7L v8, but there was a 4.3 v6 as well as 5.0L and 5.7 L v8' gassers and the 6.5L diesel.

This is from a 2010 manual, but it's likely the same as your '08 (you might want to verify)
"For all 4.3L, 4.8L and 5.3L 1500 Series applications, the proper level is 0.04 inches to 0.75 inches (1.0mm to 19.0 mm) below the bottom of the filler hole, located on the rear axle. Add only enough fluid to reach the proper level."
Earier models the correct level was even less.
This is from '04:
"The proper level for the 1500 Series is from 5/8 inch to 1 5/8 inch (15 mm to 40 mm) below the bottom of the filler plug hole."

I do turn down the dash dimmer as much as possible since it greatly improves the night time visibility (when away from town lights)
I wish it could be turned down further.
(my recollection from 'back in the day' was that the dash lights could be turned off completely if desired)
My other pet peeve is that with it set the way I want for rural night time driving, it won't be bright enough for daylight.
It should be smart enough to save as setting for when in daylight mode and a separate one for when it is in night mode.
I also would like to be able to turn down the backlight on the steering wheel controls.

Remote start won't work if there is any CEL/MIL active.
Also won't work if the hood is not closed, or if the key is in the ignition.
Glowplug failure will set a CEL/MIL and cause no remote start.
When the key is used after the remote doesn't work, is the light on?

Tow/haul gets trans temp in place of voltmeter on a denali.
On the others go to 'options' > 'info pages,' and then turn on the trans temp page.
It will now be available for scrolling to with the other pages.
Yes, it's in the manual.

Allison was a division of GM when they developed the transmission for behind the dmax and the 8.1.
(Yes, it's been updated several times since, to handle the extra torque. The change to 6 speed from 5 was a new valve body to provide a new combination using the existing gearing, and of course TCM changes. 1 - 5 are the same ratios in the 5 spd and 6 spd. )